1. Field of the Invention
The present invention relates to current mode electronic circuitry, and particularly to a complimentary metal-oxide semiconductor (CMOS) logarithmic current generator.
2. Description of the Related Art
A logarithmic function is a non-linear function in which the output is proportional to the logarithm of the input. The circuits performing such a function are typically widely used in many applications, these include but are not limited to medical equipment, instrumentation, telecommunication, active filters, disk drives and neural networks, for example.
Many approaches to the design of a logarithmic circuit have been reported in the literature. An existing type of CMOS current-mode logarithmic circuit produces the logarithmic of an input greater than unity and generally has a limited dynamic range. In addition, typically an existing type of CMOS current-mode logarithmic circuit has relatively no gain controllability and uses some passive elements. Other realizations of an existing type of CMOS current-mode logarithmic circuit typically have at least one of the following drawbacks. These drawbacks include, for example, absence of low voltage operation capability, a limited dynamic range, employment of bipolar junction transistor (BJT) transistors, does not enjoy a current-mode, cannot realize a true logarithmic function circuit where the ratio is larger or smaller than unity, temperature dependent, relatively high power consumption, generally no controllability, and, to some extent, linearity error is high, use passive elements, i.e. resistors, and general complexity of the circuit.
Thus, a CMOS logarithmic current generator addressing the aforementioned problems is desired.